Communication apparatus and method for performing inter-vehicular communication

ABSTRACT

A communication apparatus for inter-vehicular communication according to the present invention includes: a network state estimating unit configured to estimate network state information indicating a current network state based on driving information and channel state information of neighboring vehicles; a network access controller configured to control whether to transmit a message based on the network state information; a transmission scheduler configured to control a transmission time point of the message based on the network state information; and a transmission buffer unit configured to delay transmission of the message according to the control of the transmission time point of the transmission scheduler.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/904,174 filed Feb. 23, 2018 which is acontinuation of U.S. patent application Ser. No. 15/202,419 filed Jul.5, 2016, which is a continuation of U.S. patent application Ser. No.14/250,465 filed Apr. 11, 2014 which claims priority to and the benefitof Korean Patent Application No. 10-2013-0147485 filed in the KoreanIntellectual Property Office filed on Nov. 29, 2013, the disclosures ofwhich are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a communication apparatus and methodfor inter-vehicular communication, and more particularly, to acommunication apparatus and method for a safety driving service using aninter-vehicular communication technology.

BACKGROUND

Recently, research on a safety driving service (cooperative collisionavoidance, forward collision warning, lane change, and the like) usingan inter-vehicular communication technology, such as IEEE 802.11P hasbeen actively conducted. The purpose of the vehicle safety drivingservice is to provide a driver with a safer and more pleasant drivingenvironment by inducing safe driving of a vehicle and improving atraffic congestion situation by monitoring a driving situation in realtime through inter-vehicular short-range wireless communication.

The vehicle safety driving service generally has a function ofperiodically broadcasting a vehicle safety message to neighboringvehicles. The vehicle safety message basically includes a vehiclelocation vector and a time stamp, such as a location, a speed, and amovement direction of a vehicle. This enables each vehicle to recognizecurrent driving situations of neighboring vehicles in real time, andrapidly responds to a dangerous situation, thereby helping to prevent anaccident.

Accordingly, one of the significant factors for determining reliabilityof the safety driving service is reliable transception of a safetymessage. However, in a traffic congestion region in which there is a lotof vehicles, a channel load of a wireless network is rapidly increaseddue to transmission of the safety message without control, so that anetwork congestion phenomenon, such as an unlimited increase in achannel access delay or a sharp increase in a packet loss, is generated.The phenomenon may cause a fatal defect to the safety driving serviceclose to a life of a driver.

SUMMARY

One aspect of the present invention provides a communication apparatusand method capable of performing congestion control, which may satisfyrequirements of an application service while avoiding a networkcongestion situation in inter-vehicular communication.

An aspect of the present invention provides a communication apparatusfor inter-vehicular communication, including: a network state estimatingunit configured to estimate network state information indicating acurrent network state based on driving information and channel stateinformation of neighboring vehicles; a network access controllerconfigured to control whether to transmit a message based on the networkstate information; a transmission scheduler configured to control atransmission time point of the message based on the network stateinformation; and a transmission buffer unit configured to delaytransmission of the message according to the control of the transmissiontime point of the transmission scheduler.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density corresponding to apredetermined distance range from a driver's own vehicle.

The predetermined distance range may be determined according to whethera change in at least one of the packet error rate, the channel busyratio, and the vehicle density for each distance range from the driver'sown vehicle exceeds a predetermined threshold value.

The network access controller may determine a transmission probabilityaccording to at least one of the pack error rate and the channel busyratio, and transmit a message according to the determined transmissionprobability.

The network access controller may determine the transmission probabilityaccording to a tracking error rate of the vehicle.

The transmission scheduler may calculate a delay time according to atleast one of the packet error rate and the vehicle density, and thetransmission buffer unit may delay transmission of the message by thecalculated delay time.

The transmission scheduler may determine transmission power or a datarate of the message according to at least one of the packet error rateand the vehicle density.

The transmission scheduler may determine the transmission poweraccording to a distance of a tracking target vehicle.

The transmission scheduler may determine lengths of time slots forming atime frame according to the determined data rate, determine an arbitraryidle time slot among the time slots forming the time frame as a timeslot to transmit the message, and calculate a delay time correspondingto the determined time slot.

The transmission buffer unit may delay transmission of the message bythe calculated delay time.

Another aspect of the present invention provides a communication methodfor inter-vehicular communication, including: estimating network stateinformation indicating a current network state based on drivinginformation and channel state information of neighboring vehicles;controlling whether to transmit a message based on the network stateinformation; controlling a transmission time point of the message basedon the network state information; and delaying transmission of themessage according to the control of the transmission time point.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density corresponding to apredetermined distance range from a driver's own vehicle.

The predetermined distance range may be determined according to whethera change in at least one of the packet error rate, the channel busyratio, and the vehicle density for each distance range from the driver'sown vehicle exceeds a predetermined threshold value.

The controlling whether to transmit may determine a transmissionprobability according to at least one of the pack error rate and thechannel busy ratio, and transmit a message according to the determinedtransmission probability.

The controlling whether to transmit may determine the transmissionprobability according to a tracking error rate of the vehicle.

The controlling a transmission time point may calculate a delay timeaccording to at least one of the packet error rate and the vehicledensity, and the delaying may delay transmission of the message by thecalculated delay time.

The controlling a transmission time point may determine transmissionpower or a data rate of the message according to at least one of thepacket error rate and the vehicle density.

The controlling a transmission time point may determine the transmissionpower according to a distance of a tracking target vehicle.

The controlling a transmission time point may determine lengths of timeslots forming a time frame according to the determined data rate,determine an arbitrary idle time slot among the time slots forming thetime frame as a time slot to transmit the message, and calculate a delaytime corresponding to the determined time slot.

The delaying may delay transmission of the message by the calculateddelay time.

According to embodiments of the present invention, whether to transmit amessage and a transmission time point of the message may be controlledconsidering a network state in inter-vehicular communication, therebysatisfying requirements of an application service while avoiding anetwork congestion situation.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a communicationapparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a detailed configuration of a networkstate estimating unit 110 according to an embodiment of the presentinvention.

FIG. 3 is a table illustrating an example of a lookup table managed in avehicle information table 115.

FIG. 4 is a table illustrating one example of a lookup table managed bya network state profiling unit 117.

FIG. 5 is a diagram illustrating a detailed configuration of a networkaccess controller 120 according to an embodiment of the presentinvention.

FIG. 6 is a diagram illustrating a detailed configuration of atransmission scheduler 130 according to an embodiment of the presentinvention.

FIG. 7 is a diagram illustrating an example of a time frame and a timeslot managed in a time slot table 133.

FIG. 8 is a diagram illustrating a detailed configuration of atransmission buffer unit 140 according to an embodiment of the presentinvention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of aspects of the invention. The specific designfeatures of the present invention as disclosed herein, including, forexample, specific dimensions, orientations, locations, and shapes willbe determined in part by the particular intended application and useenvironment.

In the figures, reference numbers refer to the same or equivalent partsof embodiments of the present invention throughout the several figuresof the drawing.

DETAILED DESCRIPTION

Hereinafter, embodiments according to the present invention will bedescribed in detail with reference to the accompanying drawings. First,in denoting reference numerals to constitutional elements of respectivedrawings, the same elements will be designated by the same referencenumerals although they are shown in different drawings. In the followingdescription of the present invention, a detailed description of knownconfigurations or functions incorporated herein will be omitted when itis determined that the detailed description may make the subject matterof the present invention unclear. Embodiments of the present inventionwill be described below, but the technical spirit of the presentinvention is not limited thereto and may be modified and variouslyimplemented by those skilled in the art.

FIG. 1 is a diagram illustrating a configuration of a communicationapparatus according to an embodiment of the present invention. Thecommunication apparatus includes an application layer 10 providing anapplication service, a facility layer 20 performing a threat detectionfunction, a congestion control function, and the like, and a lower layer30. The lower layer 30 may include, for example, a network layer, a datalink layer, and a physical layer.

The facility layer 20 includes a threat detection unit 200 trackingvehicles and detecting a threat based on messages received fromneighboring vehicles, and a congestion controller 100 performing thecongestion control function, such as management of a state of a networkformed of neighboring vehicles and control of transmission of a messagetransceived for an application service.

The congestion controller 100 includes a network state estimating unit110, a network access controller 120, a transmission scheduler 130, anda transmission buffer unit 140.

The network state estimating unit 110 estimates network stateinformation indicating a current network state based on drivinginformation and channel state information about the neighboring vehiclesrecognized through the messages received from the neighboring vehicles.

The network access controller 120 controls whether to transmit a messagetransmitted from an application service based on the network stateinformation from the network state estimating unit 110.

The transmission scheduler 130 controls a transmission time point of themessage based on the network state information from the network stateestimating unit 110.

The transmission buffer unit 140 transfer-delays the message by delayingtransmission of the safety message according to control of thetransmission time point by the transmission scheduler 130.

In embodiments of the present invention, the message is periodically(for example, 100 ms) generated by the application service, and thegenerated message is transmitted or discarded through the network accesscontroller 120, and transfer-delayed through the transmission scheduler130 and the transmission buffer unit 140.

FIG. 2 is a diagram illustrating a detailed configuration of the networkstate estimating unit 110 according to an embodiment of the presentinvention. The network state estimating unit 110 includes a PERcalculating unit 111, a table update unit 113, a vehicle informationtable 115, and a network state profiling unit 117.

The vehicle information table 115 maintains and manages drivinginformation and change state information about each vehicle, forexample, an identification (remote vehicle ID (RVID)), a location, aspeed, a direction, a distance, a time stamp, a packet error rate (PER),a received signal strength indicator (RSSI) of each vehicle, in realtime based on the messages received from the neighboring vehicles. FIG.3 is a table illustrating an example of a lookup table managed in thevehicle information table 115.

The table update unit 113 updates the vehicle information table 115whenever the message is received or periodically based on a PER of eachvehicle calculated by the PER calculating unit 111 to be described belowand contents of a message received through a V2X communication module 40included in the vehicle. When a certain entry of the vehicle informationtable 115 is not updated for a predetermined time, the table update unit113 deletes the corresponding entry.

The PER calculating unit 111 calculates a PER of each vehicle based onthe contents of the message received through the V2X communicationmodule 40. The PER calculating unit 111 may calculate a PER of acorresponding vehicle by using a message counter corresponding to amessage for each vehicle. For example, the PER of the vehicle may becalculated through an Equation below. The Equation below represents aPER per second considering that the message generated by the applicationservice generally includes the message counter, and the message counterhas a value between, for example, 0 to 127, and is circularly assigned.

$\begin{matrix}{{PER}_{RVi} = \left\{ \begin{matrix}\begin{matrix}{\frac{\sum\left( {{Current}_{RVi} - {Previous}_{RVi} - 1} \right)}{{{Current}_{RVi} - {Init}_{RVi} + 1}},} \\{{Current}_{RVi} > {Previous}_{RVi}}\end{matrix} \\\begin{matrix}{\frac{\sum\left( {{Current}_{RVi} - {Previous}_{RVi} + 127} \right)}{{{Current}_{RVi} - {Init}_{RVi} + 1}},} \\{{Current}_{RVi} > {Previous}_{RVi}}\end{matrix}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, RV_(i) indicates an i^(th) vehicle, and PERRV_(i) indicates a PERof the i^(th) vehicle. CurrentRV_(i) indicates a message counter of acurrently received message, and PreviousRV_(i) indicates a messagecounter of a message received immediately before the currently receivedmessage (accordingly, after the calculation of the PER each time, acurrent value of PreviousRV_(i) is changed to a value of CurrentRV_(i)immediately before currently received message). InitRV_(i) correspondsto PreviousRV_(i) every one second.

The V2X communication module 40 provides the PER calculating unit 111and the table update unit 113 with the contents of the message asdescribed above, and also calculates a channel busy ratio (CBR) in theunit of a predetermined time (for example, 50 ms) through a clearchannel assessment (CCA) function and provides the network stateprofiling unit 117 to be described below with the calculated CBR.

The network state profiling unit 117 estimates the network stateinformation indicating the current network state based on the vehicledriving information and the channel state information of the vehicleinformation table 115, and the CBR information provided from the V2Xcommunication module 40. The network state based on a driver's ownvehicle is changed in real time according to a movement environment(fading, a multipath, fluidity, and the like) of the vehicle, and thenetwork state profiling unit 117 profiles the current network state andestimates information representing the state as the network stateinformation.

In embodiments of the present invention, the network state profilingunit 117 calculates a PER, a CBR, and a vehicle density (hereinafter,referred to as a “Density”) of a network within a corresponding distancerange (that is, a network formed of nodes within the correspondingdistance range) for each predetermined distance range based on adriver's own vehicle, based on the vehicle driving information and thechannel state information of the vehicle information table 115 and theCBR information. For example, when it is assumed that a distance unit is10 m, the network state profiling unit 117 calculates a PER, a CBR, anda Density of the network at each of a distance range of 10 m, a distancerange of 20 m, and a distance range of 30 m.

The PER of the network may be calculated by an average of PER values ofvehicles within the corresponding distance range. The Density of thenetwork may be calculated by a ratio of the number of vehicles withinthe corresponding distance range and an area of the correspondingdistance range.

The CBR of the network may be calculated by a maximum value among CBRvalues measured in nodes included in the corresponding network. To thisend, in embodiments of the present invention, each of the nodes insertsthe CBR value measured by each node into the message and transmits themessage, thereby sharing the CBR value. The CBR of the network may berepresented by Equation 2 below.

CBR_(net)=MAX[CBR_(i)]  [Equation 2]

Here, CBR_(i) indicates a CBR value measured in an i^(th) node(including the node itself) of a corresponding network.

The network state profiling unit 117 may calculate a PER, a CBR, and aDensity for each predetermined distance range as described above, andmaintain/mange the calculated PER, CBR, and Density in a form of alookup table as illustrated in FIG. 4.

When the PER, the CBR, and the Density are given for each networkspecified by the distance range as described above, there may incur aphenomenon that the PER, the CBR, and the Density are remarkablyincreased in a specific network. For example, the PER value in thenetwork within the distance range of 40 m is a very small valuecorresponding to 0.1, but the PER value in the network is increased to0.5 in the network within the distance range of 50 m, or the Density inthe network within the distance range of 40 m is 5, but the PER value inthe network is increased to 15 in the network within the distance rangeof 50 m. This means that network congestion is relatively less in thedistance range of 40 m, but when the distance range exceeds 50 m, thenetwork congestion is sharply increased.

Accordingly, the network state profiling unit 117 searches for adistance range (network) in which at least one value of the PER, theCBR, and the Density is remarkably distinguished, and estimates the PER,the CBR, and the Density of a network immediately before thedistinguishment as the network state information indicating the currentnetwork state. Whether the values of the PER, the CBR, and the Densityare remarkably distinguished may be determined according to whetherΔPER, ΔCBR, and ΔDensity, which are differences between the PER, theCBR, and the Density of a specific distance range and the PER, the CBR,and the Density of a next distance range, exceed predetermined thresholdvalues. Whether the network is distinguished may be determined based onwhether any one of ΔPER, ΔCBR, and ΔDensity exceeds the threshold value,and may also be determined based on whether all of ΔPER, ΔCBR, andΔDensity exceed the threshold values.

FIG. 5 is a diagram illustrating a detailed configuration of the networkaccess controller 120 according to an embodiment of the presentinvention. The network access controller 120 includes a transmissionprobability calculating unit 121 and a transmission controller 123.

In embodiments of the present invention, the threat detection unit 200calculates tracking error information, for example, a tracking errorrate, and provides the calculated the tracking error information duringa process of tracking the neighboring vehicles.

The transmission probability calculating unit 121 calculates a messagetransmission probability based on the tracking error information fromthe threat detection unit 200 and the network state information from thenetwork state estimating unit 110. The transmission controller 123determines whether to transmit or discard the message according to thecalculated transmission probability.

When the network state is poor, it is necessary to decrease thetransmission of the message, so that the transmission probability needsto be decreased, and when the tracking error rate is large, moremessages are required for accurate tracking, so that the transmissionprobability needs to be increased. Accordingly, in embodiments of thepresent invention, the PER and the CBR, which are the network stateinformation from the network state estimating unit 110 and the trackingerror rate from the threat detection unit 200 are used as a referencefor determining the transmission probability.

As an example, the transmission probability calculating unit 121 maydefine a transmission probability corresponding to the PER and CBRvalues serving as the reference, and decrease the transmissionprobability by a predetermined rate whenever the PER and CBR values fromthe network state estimating unit 110 exceed predetermined thresholdvalues. The transmission probability calculating unit 121 may define atransmission probability corresponding to the tracking error rateserving as the reference, and increase the transmission probability by apredetermined rate whenever the tracking error rate from the threatdetection unit 200 exceeds predetermined threshold values.

As another example, a calculation formula of calculating a transmissionprobability according to the network state information and the trackingerror rate is predefined, so that the transmission probabilitycalculating unit 121 may also calculate the transmission probabilityaccording to the calculation formula. In this case, different weightsmay be assigned to the PER, the CBR, and the tracking error rate, andfor example, a transmission probability PTx may be calculated byEquation 3 below.

p _(Tx)=1−(PER_(net) ×w ₁+CBR_(net) ×w ₂+(1−TE_(net))×w ₃),

1=w ₁ +w ₂ +w ₃  [Equation 3]

Here, PER_(net), CBR_(net), and TE_(net) indicate a PER, a CBR, and atracking error rate of a corresponding network, respectively, and w₁,w₂, and w₃ indicate weights corresponding to a PER, a CBR, and atracking error rate, respectively. Values of w₁, w₂, and w₃ may bepredefined.

When a message is transmitted from the safety message generating unit11, the transmission controller 123 generates a random number between 0and 1, and when the random number is larger than the transmissionprobability from the transmission probability calculating unit 121, thetransmission controller 123 transmits the message to the transmissionscheduler 130, and when the random number is not larger than thetransmission probability, the transmission controller 123 discards(deletes) the message. Accordingly, the message periodically generatedby the safety message generating unit 11 is transmitted to the outsideas the transmission probability calculated by the transmissionprobability calculating unit 121.

FIG. 6 is a diagram illustrating a detailed configuration of thetransmission scheduler 130 according to an embodiment of the presentinvention. The transmission scheduler 130 includes a transmission powerand data rate determining unit 131, a time slot table 133, a time slogdetermining unit 135, and a transmission delay calculating unit 137. Thetransmission scheduler 130 determines a time frame for transmitting themessage based on the vehicle tracking information (for example, alocation and a distance of a tracking target vehicle, and a trackingerror rate) provided from the threat detection unit 200 and the networkstate information provided from the network state estimating unit 110,and determines a delay time for a delay-transfer based on the timeframe.

The transmission power and data rate determining unit 131 determinestransmission power and a data rate of the message based on the distanceof the tracking target vehicle (for example, a maximum distance with thetracking target vehicle) provided from the threat detection unit 200 andthe PER and the Density provided from the network state estimating unit110.

When the network state is poor, the transmission distance needs to bedecreased (that is, transmission power is decreased), or a transmissiontime (time for transmission) needs to be decreased. When the distancewith the tracking target vehicle is large, the transmission distanceneeds to be increased. In the meantime, the transmission time isinversely proportional to the transmission rate, that is, the data rate.Accordingly, the transmission power and data rate determining unit 131determines the transmission power and the data rate so that, as the PERvalue, the CBR value, or the Density value of the network stateinformation is large, the transmission power is decreased or the datarate is increased. The transmission power and data rate determining unit131 determines the transmission power so that, as the distance with thetracking target vehicle is large, the transmission power is increased.The determination of the transmission power and the data rate may bedetermined for each time frame to be described below.

As one example, the transmission power and data rate determining unit131 may define transmission power and data rates corresponding to thevalues of the PER, the CBR, the Density, and the tracking distanceserving as the reference, and decrease the transmission power by apredetermined rate or increase the data rate by a predetermined ratewhenever the values of the PER, the CBR, and the Density from thenetwork state estimating unit 110 exceed the predetermined thresholdvalues. The transmission power and data rate determining unit 131 mayincrease the transmission power by a predetermined rate whenever a valueof the tracking distance exceeds predetermined threshold values. Thevalue of the transmission power is provided to the V2X communicationmodule 40, and the value of the data rate is provided to the safetymessage generating unit 11, so that the message is encoded at thecorresponding data rate and the message is transmitted with thecorresponding transmission power.

The time slot table 133 maintains/manages a virtual time frame fortransmitting the message and information about time slots within thetime frame. The time slot determining unit 135 defines time slots withinthe time frame, and determines a time slot to transmit the message amongthe time slots.

FIG. 7 is a diagram illustrating an example of a time frame and a timeslot managed in the time slot table 133. The time frame is a section inwhich nodes within the network transmit one or more messages, and forexample, a length of one time frame may be 100 ms. The length of thetime slot is determined according to a transmission time of one message.That is, the transmission time corresponding to a data rate of themessage is a length of the time slot. Accordingly, the time slotdetermining unit 135 determines a length of the time slot correspondingto the value of the data rate provided from the transmission power anddata rate determining unit 131, and divides the section of the timeframe into time slots to form the time frame. For example, when a lengthof the time frame is 100 ms, and the length of the time slot is 10 ms,the time frame is formed of 10 time slots. The time slot determiningunit 135 may detect whether a message is received through the V2Xcommunication module 40 (for example, a start point and an end point ofthe received message), and discriminate a time slot currently receivingthe message from a time slot currently receiving no message and managetime slots. For example, as illustrated in FIG. 7, the time slotcurrently receiving the message is expressed by “1” (busy slot), and anidle time slot currently receiving no message is expressed by “0” (idleslot), so that the corresponding information may be maintained in thetime slot table 133. The time slot table may be periodically updated.For example, whenever 10 time frames elapse, the time frame may beupdated.

In order to prevent a collision, the message needs to be transmittedthrough the time slot currently receiving no message (that is, the idlestate). Accordingly, the time slot determining unit 135 determines oneamong the time slots in the idle state as a time slot to transmit themessage. For example, the time slot determining unit 135 may randomlyselect one among the time slots in the idle state.

The transmission delay calculating unit 137 calculates a delay timecorresponding to the time slot determined by the time slot determiningunit 135. The delay time may be calculated according to an order of thedetermined time slot in the time frame. The calculated delay time valueis provided to the transmission buffer unit 140 together with themessage from the network access controller 120.

FIG. 8 is a diagram illustrating a detailed configuration of thetransmission buffer unit 140 according to an embodiment of the presentinvention. The transmission buffer unit 140 includes a messagecontroller 141 and a message buffer 143.

The message transmitted from the transmission scheduler 130 is basicallystored in the message buffer 143. When the message is received, themessage controller 141 first identifies whether the message is stored inthe message buffer 143. When the message is not stored in the messagebuffer 143, the message controller 141 stores the received message inthe message buffer 143, and delays the message for the delay timeprovided from the transmission scheduler 130, and then transmits themessage stored in the message buffer 143 to the lower layer 30.

When the message is stored in the message buffer 143, the messagecontroller 141 deletes the message stored in the message buffer 143,stores the received message in the message buffer 143, delays themessage for the delay time provided from the transmission scheduler 130,and then transmits the message stored in the message buffer 143 to thelower layer 30. As described above, the message controller 141 deletesthe message stored in the message buffer 143 and transmits the newmessage, so that the newest information is always provided to theneighboring vehicles.

According to embodiments of the present invention, network stateinformation about a network within a corresponding distance range isobtained for each distance range, and current network state informationis estimated based on a section in which the network state informationis remarkably changed, thereby effectively controlling a transmissionprobability of a message, message transmission scheduling, and the likeby considering a network congestion state changed in real time.Transmission power or a data rate is adjusted by using the network stateinformation and vehicle tracking information, thereby improvingstability of an application service. It is possible to effectivelyadjust a channel load and perform improved congestion control through avirtual time frame and time slot.

Next, a method of operating the communication apparatus of FIG. 1 willbe described. The method will be described with reference to FIG. 1.

First, the network state estimating unit 110 estimates network stateinformation indicating a current network state based on drivinginformation and channel state information of neighboring vehicles.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density.

The network state information may include at least one of a packet errorrate, a channel busy ratio, and a vehicle density corresponding to apredetermined distance range from a driver's own vehicle.

The predetermined distance range may be determined according to whethera change in at least one of the packet error rate, the channel busyratio, and the vehicle density for each distance range from the driver'sown vehicle exceeds a predetermined threshold value.

When the network state information is estimated by the network stateestimating unit 110, the network access controller 120 controls whetherto transmit a message based on the network state information, and thetransmission scheduler 130 controls a transmission time point of themessage based on the network state information.

The network access controller 120 may determine a transmissionprobability according to at least one of the pack error rate and thechannel busy ratio, and transmit a message according to the determinedtransmission probability.

The network access controller 120 may determine the transmissionprobability according to a tracking error rate of the vehicle.

The transmission scheduler 130 may calculate a delay time according toat least one of the packet error rate and the vehicle density.

The transmission scheduler 130 may determine transmission power or adata rate of the message according to at least one of the packet errorrate and the vehicle density.

The transmission scheduler 130 may determine the transmission poweraccording to a distance of a tracking target vehicle.

The transmission scheduler 130 may determine lengths of time slotsforming a time frame according to the determined data rate, determine anarbitrary idle time slot among the time slots forming the time frame asa time slot to transmit the message, and calculate a delay timecorresponding to the determined time slot.

After the transmission scheduler 130 controls a transmission time pointof the message, the transmission buffer unit 140 delays transmission ofthe message according to the control of the transmission time point.

The transmission buffer unit 140 may delay transmission of the messageby the calculated delay time.

Meanwhile, embodiments according to the present invention may beimplemented in the form of program instructions that can be executed bycomputers, and may be recorded in computer readable media. The computerreadable media may include program instructions, a data file, a datastructure, or a combination thereof. By way of example, and notlimitation, computer readable media may comprise computer storage mediaand communication media. Computer storage media includes both volatileand nonvolatile, removable and non-removable media implemented in anymethod or technology for storage of information such as computerreadable instructions, data structures, program modules or other data.Computer storage media includes, but is not limited to, RAM, ROM,EEPROM, flash memory or other memory technology, CD-ROM, digitalversatile disks (DVD) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium which can be used to store the desired informationand which can accessed by computer. Communication media typicallyembodies computer readable instructions, data structures, programmodules or other data in a modulated data signal such as a carrier waveor other transport mechanism and includes any information deliverymedia. The term “modulated data signal” means a signal that has one ormore of its characteristics set or changed in such a manner as to encodeinformation in the signal. By way of example, and not limitation,communication media includes wired media such as a wired network ordirect-wired connection, and wireless media such as acoustic, RF,infrared and other wireless media. Combinations of any of the aboveshould also be included within the scope of computer readable media.

As described above, certain embodiments have been described andillustrated in the drawings and the specification. Certain embodimentswere chosen and described in order to explain certain principles of theinvention and their practical application, to thereby enable othersskilled in the art to make and utilize various embodiments of thepresent invention, as well as various alternatives and modificationsthereof. As is evident from the foregoing description, certain aspectsof the present invention are not limited by the particular details ofthe examples illustrated herein, and it is therefore contemplated thatother modifications and applications, or equivalents thereof, will occurto those skilled in the art. Many changes, modifications, variations andother uses and applications of the present construction will, however,become apparent to those skilled in the art after considering thespecification and the accompanying drawings. All such changes,modifications, variations and other uses and applications which do notdepart from the spirit and scope of the invention are deemed to becovered by the invention which is limited only by the claims whichfollow.

What is claimed is:
 1. A communication apparatus for inter-vehicularcommunication, comprising: a network state estimating unit configured toestimate network state information indicating a current network statebased on driving information and channel state information ofneighboring vehicles; a network access controller configured to controlwhether to transmit a message based on the network state information; atransmission scheduler configured to control a transmission time pointof the message based on the network state information; and atransmission buffer unit configured to delay transmission of the messageaccording to the control of the transmission time point of thetransmission scheduler.
 2. The communication apparatus of claim 1,wherein the network state information includes at least one of a packeterror rate, a channel busy ratio, and a vehicle density.
 3. Thecommunication apparatus of claim 2, wherein the network stateinformation includes at least one of a packet error rate, a channel busyratio, and a vehicle density corresponding to a predetermined distancerange from a driver's own vehicle.
 4. The communication apparatus ofclaim 3, wherein the predetermined distance range is determinedaccording to whether a change in at least one of the packet error rate,the channel busy ratio, and the vehicle density for each distance rangefrom the driver's own vehicle exceeds a predetermined threshold value.5. The communication apparatus of claim 2, wherein the network accesscontroller determines a transmission probability according to at leastone of the pack error rate and the channel busy ratio, and transmits amessage according to the determined transmission probability.
 6. Thecommunication apparatus of claim 5, wherein the network accesscontroller determines the transmission probability according to atracking error rate of the vehicle.
 7. The communication apparatus ofclaim 2, wherein the transmission scheduler calculates a delay timeaccording to at least one of the packet error rate and the vehicledensity, and the transmission buffer unit delays transmission of themessage by the calculated delay time.
 8. The communication apparatus ofclaim 2, wherein the transmission scheduler determines transmissionpower or a data rate of the message according to at least one of thepacket error rate and the vehicle density.
 9. The communicationapparatus of claim 8, wherein the transmission scheduler determines thetransmission power according to a distance of a tracking target vehicle.10. The communication apparatus of claim 8, wherein the transmissionscheduler determines lengths of time slots forming a time frameaccording to the determined data rate, determines an arbitrary idle timeslot among the time slots forming the time frame as a time slot totransmit the message, and calculates a delay time corresponding to thedetermined time slot.
 11. The communication apparatus of claim 10,wherein the transmission buffer unit delays transmission of the messageby the calculated delay time.
 12. A communication method forinter-vehicular communication, comprising: estimating network stateinformation indicating a current network state based on drivinginformation and channel state information of neighboring vehicles;controlling whether to transmit a message based on the network stateinformation; controlling a transmission time point of the message basedon the network state information; and delaying transmission of themessage according to the control of the transmission time point.
 13. Themethod of claim 12, wherein the network state information includes atleast one of a packet error rate, a channel busy ratio, and a vehicledensity.
 14. The method of claim 13, wherein the network stateinformation includes at least one of a packet error rate, a channel busyratio, and a vehicle density corresponding to a predetermined distancerange from a driver's own vehicle.
 15. The method of claim 14, whereinthe predetermined distance range is determined according to whether achange in at least one of the packet error rate, the channel busy ratio,and the vehicle density for each distance range from the driver's ownvehicle exceeds a predetermined threshold value.
 16. A communicationapparatus installed in a host vehicle, the apparatus comprising at leastone computing device and configured: to generate a host vehicle safetymessage of the host vehicle comprising an identification of the hostvehicle, location information of the host vehicle, a speed of the hostvehicle, a moving direction of the host vehicle, and a first messagecounter of the first vehicle safety message; to receive vehicle safetymessages from nearby vehicles, each vehicle safety message comprisingidentification of a nearby vehicle transmitting the particular vehiclesafety message, location information of the nearby vehicle, a speed ofthe nearby vehicle, a movement direction of the nearby vehicle, a timestamp, and a message counter of the particular vehicle safety message,to estimate a probability of successful reception of the host vehiclesafety message at the nearby vehicles, to determine, based on theestimated probability, whether to broadcast the host vehicle safetymessage of the host vehicle, to compute a first delay time forbroadcasting the host vehicle safety message, to store the host vehiclesafety message in a buffer memory, and subsequent to temporarily storingand computing the first delay time, to broadcast the first vehiclesafety message of the host vehicle according to the first delay time.